That's not what "sincerity" means. Also, by that definition, his protection of Uka is insincere, since it's about his own merits and greed. That also makes him a hypocrite, which is the opposition to being sincere. He's talking about altruism.
"Is everyone like this?"
He says after comparing two people.
She's right to get the chills. I mean, he literally calls her the devil.
Smiling and forgiving are not the same thing.
Truck-kun's in this manga too.
Sure, pick up a coin in front of a truck. Talk about situational awareness.
Yeah, brother's still the worst character. Entitled, moronic, and attention grabbing. And not in a fun way like most other characters.